Satellite Dish Connection

[prpr]

if you connect a TV sat tuner and (say) a sat PVR tuner via a passive splitter to a single LNB O/P, which one wins in the control of the LNB?

Who knows. If one says 14V and the other says 18V then you are going to be sinking current one way or the other, which is bad really, and one of them will not be getting what it expects.
Don't ever do it without a DC block on one port!

 

[Black Hole]

My understanding is that some of the control is implemented by tones - so LF AC switched blocking/pass-through is also required.

 

[grahamlthompson]

You're right, I didn't. I incorrectly assumed that a satellite tuner pass-through wouldn't fiddle about enabling/disabling local or downstream power-and-command injection on the uplink (which is quite demanding. technically, and I wouldn't have expected to be a common requirement).

However, the benefit of a forum is that incorrect "facts" are easily corrected, and I see no reason to be sarky about it. Where I get snippy is when people refuse to acknowledge they are wrong.

Why didn't you simply say you weren't sure. You constantly state assumptions as facts about kit you clearly have no experience at all. It's misleading to others who assume you actually know what you are posting about, and what's more makes you look rather foolish. If you aren't sure why not just say so in the first place ?

As to quite demanding that is complete crap. All it takes is a direct link from the input coax core to the loop out core when the box is in sby. I would be amazed if all satellite boxes with loop out don't do exactly the same.

 

[grahamlthompson]

Who knows. If one says 14V and the other says 18V then you are going to be sinking current one way or the other, which is bad really, and one of them will not be getting what it expects.
Don't ever do it without a DC block on one port!

http://www.maplin.co.uk/p/2-way-satellite-splitter-bm90x

 

[prpr]

My understanding is that some of the control is implemented by tones - so LF AC switched blocking/pass-through is also required.

It's 22 kHz tone either on (high-band) or off (low-band). If either has the tone on then high-band will probably be selected.

 

[Black Hole]

The tone is modulated onto the phantom power, so injecting another tone (even through DC blocking) would probably be absorbed into the low-impedance of the phantom power source.

 

[Trev]

You have to use a splitter designed to pass control signals on one output only.

Yes, the splitter must be configured so that only control outputs from one tuner tries to control the LNB. I.E one of the RF output legs has to have a DC and low frequency AC block to prevent the tuner connected to it from controlling the LNB.

This is what tuner 1 out on a foxsat does when the the box is on or in recording sby.

Agreed.

A standard Sky dish will have a quad 4 output lnb

Not if you have a fairly old Sky dish. They have fitted single and twin O/P LNBs in the past.

But the whole discussion is totally irrelevant and pointless now as the OP's choice of TV has no sat tuner anyway, and he is going to do what he has always done.

 

[prpr]

The tone is modulated onto the phantom power,

Indeed.

so injecting another tone (even through DC blocking) would probably be absorbed into the low-impedance of the phantom power source.

Possibly. That's why I said "probably" in the previous message.
All in all, it is a bad thing, so the message is... don't do it.